12% MATK are calculated using base weapon damage, but let's give it a try.
Min and max MATK are (1370+3598) x 12% / 2 = (164+432) / 2 = 298 average damage, which, with an average MATK of (4640+12890)/2 = 8765, amount to an increase of a (8765+298)/8765 = 1.03 multiplier, 3%, of character's overall damage output (not counting skills calculated using base MATK, which won't benefit of it. I assume Invokers don't use skills too much).
32 agility points are 32 x 2.8 = 90(1) critical rate on an Invoker, which, given a soulcraft on back item and weapon only, will amount to an average 90 x [1+(51+54)%] = 185 critical rate (with middle-tier soulcrafts of a lv.70 back and a Zauharant weapon).
These 185 points amount to an average 185 / 4491 x 20% = 1%(2) final critical rate, which in turns leads to, with 300% critical damage and around 20% FCR at first, an increase of :
[8765 x ( (1-21%) + 21% x 3)](3) / [8765 x ( ( 1-20%) + 20% x 3)] = (1-21% + 21% x 3) / (1-20% + 20% x 3) = (0.79 + 0.63) / (0.80 + 0.60) = 1.01, 1% of the character's damage output, counting every skill.
With 500% CD(4), it would be (0.79 + 1.05) / (0.80 + 1.00) = 2%.
That's two options against one, but 3% against 1%, or at best 2%. You can trade this small increase for 32 Health along with the 32 Agility if so you wish, but Invokers have enough healing skills to survive about any assault with decent gear, without needing to invest much into this stat (Elga is out of question).
(1) : critical rate minus 15, divided by Agi. Since the formula showing in the character's info changes every few seconds...
(2) : 4491 is the critical rate cap for Invokers, 20% is the maximum FCR achieved through just CR.
(3) : average damage per hit after change divided by average damage per hit before change.
(4) : [Hero] Secmathian 5-part effect, weapon soulcraft option, Paris' wings soulcraft option, car pet, lv.20 IM weapon soulcraft option : 200 + 79 + 50 + 50 + 25 + 28 + 30 = 462% without expanding. Edit : bleh, 30% for the back. Just add cards ~_~
Edited by Homurasan, 13 January 2016 - 03:04 AM.